Add errno message in RemapAtEnd error.

Helps debugging.

Test: m
Change-Id: I3d8f213e73aebdbe4cbd607bc3d9e9f07fb9a724
diff --git a/libartbase/base/mem_map.cc b/libartbase/base/mem_map.cc
index 3dbe7b8..7a7158d 100644
--- a/libartbase/base/mem_map.cc
+++ b/libartbase/base/mem_map.cc
@@ -745,10 +745,10 @@
                                                           fd,
                                                           offset));
   if (actual == MAP_FAILED) {
-    PrintFileToLog("/proc/self/maps", LogSeverity::WARNING);
-    *error_msg = StringPrintf("map(%p, %zd, 0x%x, 0x%x, %d, 0) failed. See process "
+    *error_msg = StringPrintf("map(%p, %zd, 0x%x, 0x%x, %d, 0) failed: %s. See process "
                               "maps in the log.", tail_base_begin, tail_base_size, tail_prot, flags,
-                              fd);
+                              fd, strerror(errno));
+    PrintFileToLog("/proc/self/maps", LogSeverity::WARNING);
     return Invalid();
   }
   // Update *this.